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Excess Steam Quench / Seal Leaking From Asphalt Pumps

07/17/2017 5:29 PM

I just started working at a refinery and am working on a pump assessment for our asphalt plant. I'd like to know:

1) how to tell if we have excessive steam quench from our pumps in great detail.

2) many of the pumps have steam quench dripping down the seals and have standing water/leaked asphalt around the pump. How can I solve this issue? The pressure gauges seem to read that the quench is under correct operating conditions (max 1-2psi), so I am unsure if this is excessive quench.

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#1

Re: Excess steam quench / seal leaking from asphalt pumps

07/18/2017 1:23 AM

Depends on what type of seals you have....some are made to leak a bit, and the packing needs to changed periodically....Do you have a maintenance history on the pumps?...and are they packed type seals?

https://blog.craneengineering.net/the-basics-of-mechanical-seals

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#3
In reply to #1

Re: Excess steam quench / seal leaking from asphalt pumps

07/18/2017 12:18 PM

many of them are plan 62

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#4
In reply to #3

Re: Excess steam quench / seal leaking from asphalt pumps

07/18/2017 1:04 PM

I see that API Plan 62 doesn't really distinguish among various conditions for different pumped fluids, but the purging of oxygen from the seal face could be a primary function of the steam, maybe heat / seal housing is not important.

So then you might be able to reduce steam until you were sure no air is entering the drain connection, maybe you don't need 2 psig of steam pressure.

This source (McNally Institute) is cited in several locations:

http://www.mcnallyinstitute.com/03-html/3-6.html

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#6
In reply to #4

Re: Excess steam quench / seal leaking from asphalt pumps

07/19/2017 9:05 AM

See comment #5. I was pumping hot oil at 400F, so steam at 220F did help with cooling the seal and oxygen purging from the seal face. Depending on port sizing, pressure might be too high at 2 psi, flow should be adjusted to maybe a drip every 5-10 seconds? Again, this should be verified with a seal expert, not some stranger on the internet!

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#2

Re: Excess steam quench / seal leaking from asphalt pumps

07/18/2017 8:47 AM

Quench is used to control temperature behind the seal, if steam with asphalt, would be to keep it warm. So your steam condenses as it gives up heat to the seal cavity, and the water must escape somewhere, preferably not into the asphalt, I suspect.

So if you shoot the seal casing with perhaps an IR thermometer, that will tell you if you have enough steam, the temperature will be close to the 100C steam temperature. If not enough steam, the temperature will be lower.

The pump manufacturer's data, buried in some instruction book for the equipment, will tell you what temperature they recommend for the product you are pumping.

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#11
In reply to #2

Re: Excess steam quench / seal leaking from asphalt pumps

07/22/2017 6:04 AM

The steam quench is there to prevent coking of the asphalt when it comes into contact with air (oxygen), it has very little if any effect on the temperature "behind" the seal and in fact with hot asphalt it will have a cooling effect.

The actual pressure of the steam is difficult to control, but is very low. All that is required is sufficient steam to purge all oxygen from between the seal and the floating ring (or fixed) throttle bushing and the drain.

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#5

Re: Excess Steam Quench / Seal Leaking From Asphalt Pumps

07/19/2017 8:59 AM

Your seal supplier can be a big help with diagnostics. Years ago, I changed a seal type for a hot oil application. If I remember correctly, for that application we were only 0.5-0.6 psi on the steam quench. I suspect your steam pressure might be a bit high, but verify with some one who also wants you to be happy with the seal. Your seal supplier should be a more reliable source of technical information. Our seal supplier was very helpful providing technical data to support proper installation and setup for the hot oil pump seals. (BTW, we were able to extend seal repair intervals from 3-4 times per year to once per year. This seal salesman earned his keep by reducing our downtime and maintenance cost.)

Also, verify if your pressure gauges are accurate. Again, in my experience, very low pressure gauges in a rough industrial setting and poorly calibrated will suffer with poor accuracy.

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#7
In reply to #5

Re: Excess Steam Quench / Seal Leaking From Asphalt Pumps

07/19/2017 11:55 AM

I spoke to our flowserve guy and he basically told me to make sure the steam isn't more than 2-3psi and to eyeball the amount of steam coming from the stuffing box.

What if the steam is running at 1-2 psi but there's still a significant amount of excess steam coming out?

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#8
In reply to #7

Re: Excess Steam Quench / Seal Leaking From Asphalt Pumps

07/19/2017 12:15 PM

Are you supposed to be heating or cooling, would be one question to answer. If you blow the steam through so fast it doesn't condense, the heat transfer will be poor, which you may want, or might not want.

Also, what is the variability of your steam flow/pressure? You may not always observe high demand periods where the steam pressure might drop for longer times than you might consider acceptable, for temperature or oxidation upsets. Plant historical trend data may show you why the pressures are adjusted the way they are...

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#9
In reply to #7

Re: Excess Steam Quench / Seal Leaking From Asphalt Pumps

07/19/2017 12:36 PM

This is where it gets tricky. Per Flowserve, you will need to take a calibrated eyeball and adjust the amount of steam to a lower flow rate. I suspect this will be below 1 psi. I suspect a pressure gauge will become less useful and you will need to adjust to a visually acceptable flow of steam, maybe a light puff from the discharge port.

Initially, you will want to check this 2-3 times a day. Eventually, you will get comfortable with the operating condition and will check once a week. Make sure nobody plugs the discharge port. That defeats the purpose of the steam purge!

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#10
In reply to #7

Re: Excess Steam Quench / Seal Leaking From Asphalt Pumps

07/19/2017 12:40 PM

One more question, are you using a pressure regulator to adjust the steam pressure? In my opinion, that is the most reliable means to adjust this system. A globe valve or ball valve adjustment is not self-regulating and will need constant adjustment.

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